Electric furnace



n U W y C I/L U// .wf w m /1 Ox 7. E A N m om y QW Z B m w. SHQ H my. JM. m .w vw y Nw Dec. 25, 1923.

Patented Dec.,` 25, '1923e UNITED srarss PATENT oFFlcE.

MORRIS H. BENNETT, F WATEBBUEY, CONNECTICUT, ASSIGNOR T0 SCOVILL MANU-vFACJEU'R'ING COMPANY, A. CORPORATICN OF CONNECTICUT.

ELECTRIC FURNACE.

`Application led July 18,

To all wlwm t may concern:

Be it known that I, Mouais H. BnNNm'r, a citizen of the United States,residin at Waterbury, county of New Haven, and tate of Connecticut, haveinvented certain new and useful improvements in Electric Furnaces, fullydescribed and represented in the following specification and theaccompanyin drawings, forming apart of the Same. lus invention relatesto improvements in electric furnaces.

In electric furnaces as ordinaril constructed and in which the current1s conducted directly from electrode to charge, genera-ll speaking, theefficiency of the furnace is etermined by the amount of energy which canbe delivered to the charge in a given time.

In furnaces for melting metals havin a 2O high electrical conductivityand low resistance, and particularly such metals as tend to give olffumes in melting, this limitation is serious because, if it be attemptedto force a large quantity of energy into the furnace in a short time,exceive temperatures are produced beneath and immediately aroundv theelectrodes, the result of which 1s a tendency to burn the metal, orcause excessive fumes, or both. Further, the high temperaturesimmediately beneath or around the electrodesy audvilhe heat which isradi- .ated from the electrodes or from the zone between'electrode andcharge, raise the temperature in the furnace chamber to such an extentthat such fumes as are given oi produce excessive pressures in thefurnace chamber, particularly if it vbe of the closed or Bennett type1 YIn such furnaces, furthermore the effec- 4o tivev current heretoforeemployed has been of low frequency,.that is, approximately between fteenAand sixty cycles. This 'low frequency current, particularly where thecharge is composed of metals havin a high electrical conductivity is, asis wel -known, so distributed through the 'charge that its resultingheating effect in the charge is comparatively low. As has beenindicated, any attempt to increase the heating effect by 6osubstantially increasing the rate at which energy is introduced into thevfurnace by this effective low frequency current will result: inexcessive temperatures in the furnace, which is objectionable,particularly 191s. serial 1ro. 245,485.

Where the metals being melted tend to fume and will result in excessiveoverheating o the metal immediately around and beneath the electrodes.

It is the object of this invention to employ 1n furnaces such as havebeen referred to, a current of such characteristics that the heatineffect due to the passage of the current t yrough the charge will beincreased.

More specifically considered, it is the object of this invention toemploy in furnaces such as have been described an effective heatingcurrent of high frequency, the heatlng effect being increased becausethe resistance of the charge to such current is high. 4

ith these and other objects not specifically referred to in view, theinvention consists in the combination with a furnace which employs meansfor conducting the electric heatlng current directly to the charge inthe furnace, of means for supplying thereto an effective current of highfrequency.

More specifically, the invention consists in employing in au electricfurnace in which the current is conducted from electrode to charge, alow frequency generator, means being employed in connection therewith toincrease the effective frequency of current delivered to the charge.

The invention also consists in certain elements and combinations as willbe more fully described hereinafter and particularly pointed out.

Figure 1 is a da ammatic view of a furnace and connecte a paratus forcar ing the invention into e ect, the furnace being shown in section.

Figure 2 is a horizontal section of the furnace shown in Figure 1.

Figure 3 is a diagrammatic illustration by means of curves, of theresults obtained from' the construction shown in F i 1.

'lhc drawing forming a part of tL is specification illustratesdiagrammatically a furnace and roper apparatus in connection therewithor carrying the invention into effect. The furnace which has beenselected for illustration is a furnace of the closed or Bennett type,illustrated and described in connection with the application of M. H.Bennett, Serial No. 241,914, filed June 17, 1918, in which devices areshown for Bo i prevent the undue production of fumes in trodes. The

controlling the rate et heat delivery as to ing shown as connected onthe circuits. De-

lll

vices for properly positioning the electrodes to adjust thev vresistanceare shcwn,fthese consisting of drums 8, Worms 9 and worm- Wheels 10.rl`he connections from the worm drums to the electrodes are indicated atl1.

As has been indicated, furnaces which elnbody theinvention will utilizeeffective currents of high frequency, that,is, very considerably inexcess of the low frequency currents ordinarily utilized in electricfurnaces in which current is delivered directly from electrode tocharge.

As is Well-known, the use of high frequency generators for ordinaryconu'nercialv work,

such as furnace Work, presents many diff culties. rlhe expense ofinstallation of such generators is large, and the electrical losses arehigh, particularly if the current reqires to be transmitted overanyconsidera.

le length of line. Preferably, therefore, in carrying the invention intoeiect, the eective high frequency utilized in thefurnace will beobtained by increasing the eftective frequency of current derived from alow frequency generator. ln the commercialv practice of the invention,van edective high frequency of about 1200 cycles has been obtained byincreasing the edective requency of current derived from a low frequencnerator, the generator being de signe to deliver a 'current of aboutsixty cycles. y The delivery of the edective high frequency currentderived from a low frequency generator, When the high frequency isobtained in this manner, may be eciently attained by employing acondenser or condensers. Condensers of various constructions y beemployed. A condenser which has been found efficient is of theelectrolytic type and consists of a series of closely spaced aluminumplates in an electrolyte consisting of a saturated solution ofbicarbonate of soda. rl`hree such condensers are indicated at 12, 13 and1d, respectively.

e condensers employed for carrying the invention into edect may bevariously connec on the circuit. As shown, the

connection is of the if type, one set of thev plates in each cell beingconnected by a common strap 15 and the other plates in the cells beingconnected by Wires 16, 17 and 18 to the circuit wires 7, 6, 5respectively. lt `will be understood that in the construction shown,these circuits 5, 6, 7 .lead to a suitable low frequency generator ofthe polyphase uw it necessary a suitable trans- 4 indicated.

Leraars former being interposed in the circuit. As these devices areWell-known, they are not Actual commercial test of the apparatus which.has beendescribed, using a loir, frequency generator delivering acurrent of about sixty cycles and employing three condensers having acapacity of about 3200 microfarads each, has shown that a much highertem erature canl be obtained and maintained 1n the metal, and,consequently, better heating, Without undueproduction of fumes, thanwith the same apparatus withl out the condensers. This, of course, ishighlyadvantageous Where metals are being melted, the pouringtemperature of which is necessarily considerably above the vaporizingpoint. The heating effect inthe charge is increased Without increasingthe temperature inthe urnaceabove the charge, so that such fumes as aregiven olf are more readily condensed by the walls of the furnacechamber, the valuable metallic constituents which are carried by fumesbeing thus returned to the charge.

The results obtained by thus connecting a condenser into the circuit areindicated in Fig. 3; ln thi'sfigure, the upper curve, marked representsthe current in the transformer circuit and is a characteristic curveofthe current obtained from an alternating generator. The lower curvemarkedy B re resents the current in the condenser c, u c i n l circuitand 1s a characteristic hlgh frequency current curve.

tion of current rB on current A. The irregularities in curve Cindicatethe higher frequency obtained rom'this superposition.

The intermediate curve, marked C, represents' the current .in theelectric circuit due to the superposif While the invention may begisedwith furnaces of other types, it is particularly valuable in connectionwith a furnace ofV the closed or Bennett type referred to.

It will be understood that changes and variations ma be made in theparticular construction s own and described. The invention is not,therefore, togbeconlined to frequency, the. resulting current producingy improved heating eects in the furnace due to the resistance of thecharge to said current. `v

' 2. The combination with a furnacey for melting metals, said furnacehavin electrodes arranged to deliver current, irectly to the charge inthe furnace, of a low frequency generatorin circuit with the electrodes,and means ao in circuit with the electrodes for impressingl on the maincurrent a heating current of high frequency, the resulting current beingdelivered to the charge inthe furnace by the electrodes` and producingimproved heating'eifects therein due to the high resistance of thecharge to.

said current.

3. The combination with a furnace for melting metals, said furnacehaving electrodes arranged to deliver current directly to the charge inthe furnace, of a low frequency generator in circuit with theelectrodes, a condenser also in circuit with the electrodes andoperating to impress on the main heating current a heating current ofhigh frequency, the resulting current being for melting metals, of meansfor delivering current of high frequency', the resulting curi rentproducing improved heating effects in -the furnace due to the resistanceof the charge to ,said current.

8. The combination With a closed furnace for melting metals, saidfurnace having electrodes arranged to deliver current directly to thecharge in the furnace, of a lowY frequency( generator in circuit withthe electrodes, and means also in circuit with the electrodes forimpressing on the main current a heating current of high frequency, theresulting current being delivered to the charge in the furnace by theelectrodes and producing improved heating effects therein due to thehigh resistance of the charge to said current.

9. The combination with a closed furnace for melting metals, saidfurnace having electrodes arranged to deliver current directly to thecharge in the furnace, of a low frequency generator in circuit with theelectrodes, a condenser also in circuit with the electrodes andoperating to impress on the main heating current a heating current of hih frequency, the resulting current being delivered to the charge in thefurnace bythe electrodes and producing improved heating effects thereindue to the high resistance of the charge to said current.

In testimony whereof, I have hereunto set my hand.

MORRIS H. BENNETT.

